- Dynamic JPEG Image
- Dynamic PNG Image
- Barcode Size and Printer Resolution
- Threading Model
<img src="barcode.asp?image=3&type=6&data=12345678">in your HTML file and, voila, you have a Code 39 barcode image that's dynamically generated.
The advantage of the JPEG image format is that it's supported by virtually all commercial grade browsers in all their versions.
It's well-known that JPEG uses lossy image compression. BarCode/ASP generates JPEG with high quality (and low compression). The result is fairly good. However, you may see background noises when printing using Netscape; we think that's because Netscape adopts a low quality decompression approach (yes, like compression, you can specify a quality parameter for decompression, too). Fortunately, our tests show that the result is still scannable in our test conditions (300 dpi laser printer).
<img src="barcode.asp?image=1&type=6&data=12345678">Unlike JPEG, PNG uses lossless image compression and gives you high quality images. The only drawback is that PNG is only support by recent browsers (i.e., IE 4.0 or later and Netscape 4.04 or later). If you're target these browsers, we highly recommend you PNG image format.
Why Not Supporting GIF?
GIF is not supported for legal reasons. We'll support GIF when there's enough demand for it. In fact, any web site operators who use GIF generation software on their web site would need to pay a substantial amount of royalties to Unisys Coporation ($5000 as of the time this product was being made as we were told). In addition, we would also need to pay Unisys an up-front fee.
To ask BarCode/ASP to generate
the sequence for you, just call the GetHTML2
method, as demonstrated by Sample 1
and Sample 2.
You can also generate the sequence yourself in scripting languages.
You'll need then to call the EnumBarStart
and EnumBarNext methods to get the positions
and widths of the barcode bars. Sample 3
Barcode Size and Printer Resolution
The minimum barcode width on the screen is given by the
NumModules property. The barcode width
can only be a multiple (1, 2, etc.) of this minimum width. You can change the
scale factor when using barcode.asp, e.g. <img src=barcode.asp?barwidth=2>
will use a scale factor of 2;
if you script the BarCode/ASP component directly, you can
set this scale factor in MakeImage,
or EnumBarStart. While different bar
widths are in proportion on the screen, the printed version may
be different. The higher the printer resolution, the better the result
is. If the printer resolution is low, you may need to use a scale
factor of 2 or higher, so that the printed barcode is scannable.
Note that this is different from applications using directly
or DLL, in which case the barcode component has the
opportunity of tuning the barcode directly according to the
destination printer resolution.
You can also generate the sequence yourself in scripting languages. You'll need then to call the EnumBarStart and EnumBarNext methods to get the positions and widths of the barcode bars. Sample 3 demonstrates this.
If you find the barcode size too big, you can specify a
If you have to script BarCode/ASP directly, you need to know
it uses the apartment threading model,
which means that it can be used at the ASP Page and Session object
level but not at the Application object level. Typically, you would create
a BarCode object in an ASP page and delete it before the page goes
out of the scope (or has it deleted automatically if the variable holding
the object is a page level variable). To delete the object explicitly, you
set barcode = nothing
barcode is the variable holding the object.